to Chili was met with, which, with other characteristics, proved the
dust to be the same as that observed on the Atlantic. Their colour,
too, was identical; while the Sahara is a 'dazzling white sand:' hence
the dust brought across the Mediterranean by the sirocco was not
peculiar to Africa. The conclusion here arrived at was still further
verified by another sirocco-storm in May 1846, which extended to
Genoa, and bore with it a dust that 'covered the roofs of the city in
great abundance.' This, as was clearly ascertained, contained
formations identical with those which had been collected off the Cape
de Verd; and it was shewn that the dust-showers of the Atlantic, and
those of Malta and Genoa, were 'always of a yellow ochre-like
colour--not gray, like those of the kamsin, in North Africa.' The
peculiar colour of the dust was found to be caused by iron-oxide; and
from one-sixth to one-third of the whole proved to consist 'of
determinable organic parts.' In the following year, 1847, Ehrenberg
had another opportunity of testing his conclusions, in specimens of
dust which had fallen in Italy and Sicily in 1802 and 1813; the same
result came out on examination; 'several species peculiar to South
America, and none peculiar to Africa.'

Thus, omitting the two last-mentioned instances, there had been five
marked falls of dust between 1830 and 1846; how many others passed
without notice, it would now be impossible to ascertain. The showers
sometimes occur at a distance of 800 miles from the coast of Africa,
and this region lies between the parallels of 17 and 25 degrees north
latitude, and whence, as we have seen, they extend to the northern
shores of the Mediterranean. In the dust collected from these various
falls, there have been found altogether nineteen species of infusoria;
of which eight were polythalamia, seven polygastrica, and two
phytolitharia, these chiefly constituting the flint-earth portion of